Ultrasound is a diagnostic imaging technique which provides a number of significant advantages over other diagnostic methodology. Unlike imaging techniques such as nuclear medicine and X-rays, ultrasound does not expose the patient to the harmful effects of ionizing radiation. Moreover, ultrasound is relatively inexpensive and can be conducted as a portable examination.
In ultrasound imaging, sound is transmitted into a patient or animal via a transducer. When the sound waves propagate through the body, they encounter interfaces from tissues and fluids. Depending on the acoustic properties of the tissues and fluids in the body, the ultrasound sound waves are partially or wholly reflected or absorbed. When sound waves are reflected by an interface they are detected by the receiver in the transducer and processed to form an image. The acoustic properties of the tissues and fluids within the body determine the contrast which appears in the resultant image.
Magnetic resonance imaging (MRI) is a relatively new imaging technique which, unlike X-rays, does not utilize ionizing radiation. Like computed tomography, MRI can make cross-sectional images of the body, however MRI has the additional advantage of being able to make images in any scan plane (i.e., axial, coronal, sagittal or orthogonal).
MRI employs a magnetic field, radiofrequency energy and magnetic field gradients to make images of the body. The contrast or signal intensity differences between tissues mainly reflect the T1 and T2 relaxation values and the proton density (effectively, the free water content) of the tissues.
Advances have been made in recent years in diagnostic ultrasound and MRI technology. However, despite the various technological improvements, ultrasound and MRI are still imperfect tools in a number of respects, particularly with regard to the imaging and detection of disease in the liver and spleen, kidneys, heart and vasculature, including the measurement of blood flow. The ability to detect these regions and make such measurements depends on the difference in acoustic properties (ultrasound) or T1 and T2 signal intensity (MRI) between tissues or fluids and the surrounding tissues or fluids. Accordingly, contrast agents which will increase these differences between tissues or fluids and the surrounding tissues or fluids, and improve ultrasonic or magnetic resonance imaging and disease detection, have been sought. As a result of this effort, new and better contrast agents have been developed. Nonetheless, one recurrent problem with many of such contrast agents has been shelf-life stability, making long term storage a problem.
The present invention addresses these and other concerns by providing a convenient container comprising an aqueous lipid suspension phase and a gaseous phase substantially separate from the aqueous lipid suspension phase which, upon agitation prior to use, produces an excellent gas-filled liposome contrast agent for use in such applications as ultrasound or magnetic resonance imaging, as well as other uses. Since the contrast agent is prepared immediately prior to use, shelf-life stability problems are avoided.